Phase change memory is a type of non-volatile random-access memory that utilizes a detectable change in the physical state of a material as an information storage medium. For example, the phase change of a material from an amorphous state to a crystalline state or vice versa can be induced and then detected in order to store and then retrieve information. As a simplified example, a chalcogenide material can be heated and cooled in a manner that solidifies the material in an amorphous state, or the chalcogenide heated and cooled in a manner that solidifies the material in a crystalline state. Other specific heating and cooling protocols may be employed to result in solidification of the calcogenide material at different specific degrees of crystallinity across the spectrum between completely amorphous and completely crystalline states.
Once solidified, the phase change material is non-volatile. The phase change material state, whether solidified to a crystalline, semi-crystalline, amorphous, or semi-amorphous state, is thus retained until reprogrammed. This is due to the fact that, once solidified, the state of the material is not dependent upon electrical power.